I prefer an oil finish because it is spot repairable and easy. The spar varnish or urethane helps the drying process and adds protection to the finish.

STEP-BY-STEP

1. Sand
I belt sand to 120, use a random-orbit sander for 150-, 180- and 220-grit, hand-sand to 220-grit and sometimes 320. Then I polish with 0000 steel wool.

2. First coat
Straight Danish oil, ambient temperature should be above 70°. Oil each piece (case, drawers, bottoms, tops) and wipe, being careful to remove all oil. Let dry for 48 hours, and then go over all surfaces with 0000 steel wool.